Here’s a rule: Never write a sentence of the form “X not Y because Z,” such as Dave is not evil because he did what he was told. It should be either Dave is not evil, because he did what he was told, where the comma keeps the because outside the scope of the not, or Dave is evil not because he did what he was told (but for some other reason), where the because occurs next to the not, indicating that it is within its scope.
